In article ,
Rick (W-A-one-R-K-T) wrote:

Are there any construction articles around anywhere that describe an
auto-tuner similar to the LDG and SGC offerings?

I need an auto-tuner that I can control from a laptop, and set frequencies
as needed (mostly for ALE). I can do the digital design and the software
in my sleep, for an embedded microprocessor that can control all of that,
but the heavy-lifting part of the antenna tuner (all the toroids and caps
and relays) is a bit beyond my capabilities.

If there are any construction articles that I can adapt to my needs that
would be a very big help.

There was a two-part (I think) article in QST a couple of years ago
which showed a high-power external ATU with onboard microprocessor
control.

Its design was rather different from the LDG/SGC/Sunair/what-have-you
microprocessor-controlled switched-cap/inductor pi/L tuner. It
uses air-variable capacitors and a roller inductor (in a fairly
typical T-network). It doesn't implement automatic search-and-match.
Instead, it tunes from memory. You tune your radio to a specific
frequency, adjust the caps and inductor for the desired match using
up/down toggle switches, and then hit a "memorize" button, and the
controller remembers the frequency and the correct reactance settings.
On subsequent frequency changes, you just select the desired frequency
and the correct reactances are "dialed in".

Eliminating the "try lots of combinations to achieve the lowest SWR"
part of the system will greatly simplify the RF part of the
implementation... you won't need to implement the voltage and current
detectors, phase comparators, etc. needed to permit the digital logic
to measure SWR, etc. The on-board digital logic might be something as
simple as a micro which can [1] run a set of three stepper or gearhead
motors to rotate the cap and inductor shafts, and [2] read out DC
voltages from a set of potentiometers connected to the shafts.

A simple serial-port or USB protocol would then allow the PC to
determine the current settings of the reactances, and control the
motors to adjust them as needed for a new frequency. A second serial
or USB port would be used to communicate with whatever your rig is, to
either read out the frequencies being tuned, or to switch the rig to a
different frequency.

A similar system could be done with switched banks of inductors and
caps, in the usual power-of-two size hierarchy. In this case, the
micro would be just ordered to turn on or off the various relays used
to switch toroids and caps in and out of the series and shunt circuits.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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